This invention relates generally to a communication system and more specifically to a method for monitoring unused bins in a multi-channel communication system.
In order to make high data rate interactive services such as video conferencing and internet access available to more residential and small business customers, high speed data communication paths are required. Although fiber optic cable is the preferred transmission media for such high data rate services, it is not readily available in existing communications networks, and the expense of installing fiber optic cable is prohibitive. Current telephone wiring connections, which consist of twisted pair media, were not designed to support the high data rates required for interactive services such as video on demand or even high speed interconnects. In response, Asymmetrical Digital Subscriber Line (ADSL) technology has been developed to increase the transmission capabilities within the fixed bandwidth of existing twisted pair connections, allowing interactive services to be provided without requiring the installation of new fiber optic cable.
Discrete Multi-Tone (DMT) is a multi-carrier technique that divides the available bandwidth of a communications channel such as a twisted pair connection into a number of frequency sub-channels. These sub-channels are also referred to as frequency bins or carriers. The DMT technique has been adopted by the ANSI T1E1.4 (ADSL) committee for use in ADSL systems. In ADSL, DMT is used to generate 250 separate 4.3125 kHz sub-channels from 26 kHz to 1.1 MHz for downstream transmission to the end user, and 25 sub-channels from 26 kHz to 138 kHz for upstream transmission by the end user. Each bin is allocated a number of bits to send with each transmission. The number of bits allocated to an ADSL system are 0, and 2-15 bits.
Prior to transmitting real-time data with an ADSL system, an initialization process occurs. During a first portion of the initialization process, an activation and acknowledgment step occurs. It is during this step that a transmit activation tone is generated following power-up of the ADSL system. Transceiver training is the next step of the initialization process. During transceiver training, the equalization filters of the ADSL system are trained and system synchronization is achieved. Next, channel analysis and exchange are performed as part of the initialization processes. During the channel analysis and exchange, the Signal to Noise Ratio (SNR) of the channels is determined, and bit loading configuration of the bins and other configuration information is transferred.
Used and unused bins are a result of the bit loading process described above. During real-time operations, when real data is being sent, used carriers are those bins which transmit real data in order to maintain a specific data rate. Unused bins are those bins that are not needed to maintain the data rate, and therefore do not transmit real data. In one implementation of the ADSL specification, the unused bins have no transmit power associated with them. Without transmit power on unused bins, power consumption is minimized, but it is not possible to update equalizers, or measure channel characteristics of these unused bins. Therefore, once a bin was set up as unused in the initialization process, further use of the bin would be unwise to use in the future because of the unknown channel characteristics.
Other implementations of the ADSL specification allow transmit power to be associated with all unused bins simultaneous to transmission of power/user data on used bins. However, these implementations require either all bins be off, all bins be on, or some predefined number bins be on in order to allow for measurements and equalization based on data frames. Therefore, in order to assure optimal coverage of the unused channels, it would be necessary for all bins to be on in order to monitor any change in characteristics associated with these unused bins. However, such an implementation would require increased CPU power, in order to continuously transmit energy and monitor the characteristics associated with the unused bins, would cause an increase in total power needed to drive the ADSL system, and in addition, would cause interference on adjacent ADSL systems.
Therefore, a flexible method to facilitate the transmission of energy on unused bins simultaneously to transmitting real data on used bins by the transmitter, and monitoring the unused bins simultaneously to receiving real data on used bins at the receiver which overcomes the prior art problems would be beneficial.